Lithium ion secondary battery active material, lithium ion secondary battery electrode, lithium ion secondary battery, electronic device, electronic power tool, electric vehicle, and power storage system

ABSTRACT

A lithium ion secondary battery includes: a positive electrode; a negative electrode; and an electrolytic solution, at least one of the positive electrode and the negative electrode being capable of storing and releasing lithium ions, and containing an active material that satisfies predetermined conditions.

FIELD

The present technology relates to lithium ion secondary battery activematerial capable of storing and releasing lithium ions, electrodes forlithium ion secondary batteries using the active material, lithium ionsecondary batteries using the electrodes, electronic devices, electricpower tools, electric vehicles, and power storage systems using thesecondary batteries.

BACKGROUND

There is a strong demand for smaller, lighter, and longer-lifeelectronic devices such as mobile phones and portable informationterminal devices, which have become pervasive over the last years. Inthis connection, batteries, particularly secondary batteries, that aresmall and light and capable of providing high energy density have beendeveloped as power supplies. Aside from applications to these electronicdevices, the use of the secondary batteries has been investigated in avariety of other areas, including electric power tools such as anelectric drill, electric vehicles such as an electric car, and powerstorage systems such as a home power server.

Among a wide range of secondary batteries that operate under a varietyof charge and discharge principles, lithium ion secondary batteries thatprovide battery capacity by taking advantage of the storage and releaseof lithium ions are very promising for their ability to provide higherenergy density than other batteries such as lead batteries and nickelcadmium batteries.

Lithium ion secondary batteries include a positive electrode, a negativeelectrode, and an electrolytic solution. The positive electrode and thenegative electrode contain active material capable of storing andreleasing lithium ions. Typically, Li complex oxides are used as theactive material of the positive electrode (positive electrode activematerial). Typical examples of Li complex oxides include compoundshaving a laminar rock salt structure (such as LiCoO₂), compounds havinga spinel structure (such as LiMn₂O₄), and compounds having an olivinestructure such as LiFePO₄. Typical examples of the active material ofthe negative electrode (negative electrode active material) includecarbon materials such as graphite, metallic materials such as Si and Sn,and Li complex oxides such as Li₄Ti₅O₁₂. The active materials areappropriately selected according to such factors as the intended use ofthe lithium ion secondary battery.

These active materials have been studied in a variety of ways withregard to their compositions and configurations, because the types ofactive material greatly influence battery performance such as batterycapacity and cycle characteristics. Specifically, because the storageand release of lithium ions tend to be slower when using a Li complexoxide of an olivine structure as the positive electrode active materialthan when using a Li complex oxide of a laminar rock salt structure,there has been a number of proposals directed to improving the storageand release of lithium ions.

For example, JP-A-2001-110414 proposes supporting conductive fineparticles on the powder surface of lithium iron phosphate material toimprove the charge and discharge capacity for the charge and dischargeof large current. The lithium iron phosphate material is represented byLi_(z)Fe_(1−y)X_(y)PO₄ (X is Mg or the like, 0≦y≦0.3, 0<z≦1). Theconductive fine particles have a higher redox potential than the lithiumiron phosphate material.

For example, JP-A-2003-036889 proposes combining lithium transitionmetal complex oxide particles and carbon substance fine particles toobtain excellent input and output densities independent of the chargedstate. The lithium transition metal complex oxide is represented byLiMePO₄ (Me is one or more divalent transition metals).

For example, JP-A-2002-110162 proposes combining LiFe complex phosphateand carbon material, and providing a specific surface area of 10.3 m²/gor more for the complex, in order to obtain excellent electricalconductivity. The LiFe complex phosphate is represented by Li_(x)FePO₄(0<x≦1), and the complex primary particle size is 3.1 μm or less.

For example, JP-A-2004-259470 proposes producing a lithium compositemetal phosphate having a crystallite size of 35 nm or less to obtainhigh discharge capacity, using the spray-pyrolysis technique. Thelithium composite metal phosphate is represented by Li_(x)A_(y)PO₄ (A isFe or the like, 0<x<2, 0<y≦1).

For example, JP-A-2009-263222 proposes producing lithium iron phosphateparticles using a lithium raw material, a phosphorus raw material, andan iron raw material (for example, iron oxide with an average primaryparticle size of 5 nm to 300 nm), in order to obtain high capacity evenunder current load conditions. The producing method includes mixing theraw materials, adjusting the agglomerate particle size of the mixture to0.3 μm to 5 μm, and calcining the agglomerate particles under, forexample, a reducing gas atmosphere.

SUMMARY

Improving the lithium ion input-output characteristics of the activematerial is considered essential for ensuring the battery capacity andcycle characteristics of the lithium ion secondary battery. However, theattempts to improve the lithium ion input-output characteristics incases of the use of Li complex oxides of an olivine structure as thepositive electrode active material cannot be said as being sufficient.This is not only the problem when using the Li complex oxides of anolivine structure as the positive electrode active material, but theproblem when using other Li complex oxides having a laminar rock saltstructure or a spinel structure, or using the Li complex oxides as thenegative electrode active material.

Accordingly, there is a need for a lithium ion secondary battery activematerial capable of improving the lithium ion input-outputcharacteristics, a lithium ion secondary battery electrode, a lithiumion secondary battery, an electronic device, an electric power tool, anelectric vehicle, and a power storage system.

An embodiment of the present technology is directed to an activematerial for a lithium ion secondary battery capable of storing andreleasing lithium ions and satisfying the following conditions (A) to(D): (A) the active material being a Li complex oxide or a Li complexoxoacid salt that contains lithium, oxygen, and at least one of theelements of Groups 2 to 15 of the long-form periodic table; (B) theactive material containing a plurality of primary particles having aparticle size distribution (median diameter: nm) with 1 nm<D10<65 nm, 5nm<D50<75 nm, and 50 nm<D90<100 nm; (C) the active material having aplurality of pores between the plurality of primary particles, whereinthe maximum peak pore size A (nm) in a pore size distribution asmeasured by a mercury intrusion technique is 10 nm≦A≦75 nm; and (D) theratio B/A of the maximum peak pore size A (nm) and the crystallite sizeB (nm) determined from the half width of an X-ray diffraction pattern asmeasured by X-ray diffractometry is 0.5<B/A≦1.

Another embodiment of the present technology is directed to an electrodefor a lithium ion secondary battery including the lithium ion secondarybattery active material of the embodiment of the present technologydescribed above. Still another embodiment of the present technology isalso directed to a lithium ion secondary battery including a positiveelectrode, a negative electrode, and an electrolytic solution, whereinthe lithium ion secondary battery electrode of the embodiment of thepresent technology described above is used as at least one of thepositive electrode and the negative electrode. Yet another embodiment ofthe present technology is directed to an electronic device, an electricpower tool, an electric vehicle, or a power storage system using thelithium ion secondary battery of the embodiment of the presenttechnology described above.

In the lithium ion secondary battery active material, the lithium ionsecondary battery electrode, and the lithium ion secondary battery ofthe embodiments of the present technology, the active material capableof storing and releasing lithium ions satisfies the foregoing conditions(A) to (D). In this way, the lithium ion input-output characteristicscan be improved. The same effect also can be obtained in the electronicdevice, the electric power tool, the electric vehicle, and the powerstorage system using the lithium ion secondary battery of the embodimentof the present technology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view illustrating the configuration of alithium ion secondary battery (cylindrical secondary battery) using theactive material of an embodiment of the present technology.

FIG. 2 is across sectional view illustrating a magnified portion of awound electrode unit shown in FIG. 1.

FIG. 3 is a perspective view illustrating the configuration of anotherlithium ion secondary battery (laminate film secondary battery) usingthe active material of the embodiment of the present technology.

FIG. 4 is a cross sectional view of a wound electrode unit shown in FIG.3, taken at the line IV-IV.

FIG. 5 is a cross sectional view illustrating the configuration of atest secondary battery (coin-shaped secondary battery).

DETAILED DESCRIPTION

The following specifically describes embodiments of the presenttechnology with reference to the accompanying drawings. Descriptionswill be given in the following order.

1. Lithium ion secondary battery (active material for lithium ionsecondary battery, and electrode for lithium ion secondary battery)

-   -   1-1. Cylindrical secondary battery    -   1-2. Laminate film secondary battery

2. Use of lithium ion secondary battery

<1. Lithium Ion Secondary Battery> <1-1. Cylindrical Secondary Battery>

A lithium ion secondary battery of an embodiment of the presenttechnology is described first. The active material for lithium ionsecondary batteries, and the electrode for lithium ion secondarybatteries of the embodiment of the present technology are used for thelithium ion secondary battery described below.

FIG. 1 and FIG. 2 are cross sectional views illustrating theconfiguration of the lithium ion secondary battery (hereinafter, simply“secondary battery”). FIG. 2 shows a magnified portion of a woundelectrode unit 20 illustrated in FIG. 1.

[Overall Configuration of Secondary Battery]

The secondary battery is what is commonly called a cylindrical secondarybattery. The secondary battery includes a substantially hollowcylindrical battery canister 11, the wound electrode unit 20, and a pairof insulating plates 12 and 13. The wound electrode unit 20 and theinsulating plates 12 and 13 are housed inside the battery canister 11.The wound electrode unit 20 includes, for example, a positive electrode21 and a negative electrode 22 laminated and wound around via aseparator 23.

The battery canister 11 has a hollow structure with a closed end and anopen end, and is formed of, for example, Fe, Al, or alloys thereof. Thesurface of the battery canister 11 may be plated with metallic materialsuch as Ni. The pair of insulating plates 12 and 13 is disposed so as tosandwich the wound electrode unit 20 from the top and bottom, and toperpendicularly extend with respect to the rolled surface.

A battery lid 14, a safety valve mechanism 15, and a heat-sensitiveresistive element (positive temperature coefficient: PTC element) 16 areswaged to the open end of the battery canister 11 via a gasket 17. Theswaging seals the battery canister 11. The battery lid 14 is formedusing, for example, the same material used for the battery canister 11.The safety valve mechanism 15 and the heat-sensitive resistive element16 are provided on the inner side of the battery lid 14, and the safetyvalve mechanism 15 is electrically connected to the battery lid 14 viathe heat-sensitive resistive element 16. The safety valve mechanism 15cuts off the electrical connection between the battery lid 14 and thewound electrode unit 20 by the inversion of a disk plate 15A, when theinner pressure reaches a certain level as a result of, for example,internal shorting or external heat. The heat-sensitive resistive element16 prevents abnormal heating due to large current. The resistance of theheat-sensitive resistive element 16 increases with increasingtemperatures. The gasket 17 is formed using, for example, insulatingmaterial, and may be asphalt-coated.

A center pin 24 may be inserted at the center of the wound electrodeunit 20. The positive electrode 21 is connected to a positive electrodelead 25 formed of conductive material, for example, such as Al. Thenegative electrode 22 is connected to a negative electrode lead 26formed of conductive material, for example, such as Ni. The positiveelectrode lead 25 is welded to the safety valve mechanism 15, andelectrically connected to the battery lid 14. The negative electrodelead 26 is welded to the battery canister 11, and electrically connectedthereto.

[Positive Electrode]

The positive electrode 21 is structured to include, for example, apositive electrode active material layer 21B provided on at least oneside of a positive electrode collector 21A. The positive electrodecollector 21A is formed of conductive material, for example, such as Al,Ni, and stainless steel.

The positive electrode active material layer 21B includes one or morepositive electrode active materials capable of storing and releasinglithium ions. Other materials such as a positive electrode binder and apositive electrode conductive agent also may be contained, as required.

The positive electrode active material is an active material for lithiumion secondary batteries of the embodiment of the present technology. Thepositive electrode 21 containing the positive electrode active materialis an electrode for lithium ion secondary batteries of the embodiment ofthe present technology. The positive electrode active material satisfiesthe following four conditions (A) to (D) (hereinafter, simply “fourconditions”).

(A) First Condition

The positive electrode active material is a Li complex oxide or a Licomplex oxoacid salt that contains lithium (Li), at least one of theelements (M) in Group 2 to 15 of the periodic table (long form), andoxygen (O) as the constituting elements, because these compounds areelectrochemically stable, and excel in storing and releasing lithiumions. The element M is not particularly limited, as long as it is atleast one element from Group 2 to 15 of the periodic table (long form).

Specifically, the Li complex oxide has, for example, a laminar rock saltstructure or a spinel structure. A Li complex oxide having a laminarrock salt structure is, for example, a compound of the following formula(1), and a Li complex oxide having a spinel structure is, for example, acompound of the following formula (2).

Li_(a)M1O₂  (1)

(where M1 is at least one of the elements of Groups 2 to 15 of thelong-form periodic table, and a satisfies 0<a≦1.2)

Li_(b)Mn_(c)M2_(d)O₄  (2)

(where M2 is at least one of the elements of Groups 2 to 15 of thelong-form periodic table (excluding Mn), and b, c, and d satisfy 0<b≦1,0<c≦2, 0≦d<2, and c+d=2)

The M1 in equation (1) is not particularly limited, as long as it is atleast one element from Groups 2 to 15 of the long-form periodic table.For example, M1 is at least one of Ni, Co, Mn, Cu, Fe, Zn, Y, Ti, Mo,Al, Mg, B, V, Cr, Sn, Ca, Sr, and W. Specific examples of the Li complexoxide having a laminar rock salt structure include LiNiO₂, LiCoO₂,LiNi_(k)Co_(l)Mn_(m)O₂ (k+l+m=1), and LiNi_(k)Co_(l)Al_(m)O₂ (k+l+m=1).These Li complex oxides may further contain a small amount of at leastone of the candidate elements M1 above.

The M2 in equation (2) is not particularly limited, as long as it is atleast one element from Groups 2 to 15 of the long-form periodic table.For example, M2 is at least one of Co, Ni, Mg, Al, B, Ti, V, Cr, Fe, Cu,Zn, Mo, Sn, Ca, Sr, and W. Specific examples of the Li complex oxidehaving a spinel structure include LiMn₂O₄. The Li complex oxide of aspinel structure may further contain a small amount of at least one ofthe candidate elements M2 above.

The Li complex oxoacid salt is, for example, Li complex phosphate orother oxoacid salt. The Li complex phosphate has, for example, anolivine structure or some other structure. The Li complex phosphatehaving an olivine structure is, for example, a compound of the followingformula (3).

Li_(e)M3_(f)PO₄  (3)

(where M3 is at least one of the elements of Groups 2 to 15 of thelong-form periodic table, and e and f satisfy 0<e≦1, 0<f≦1)

The M3 in equation (3) is not particularly limited, as long as it is atleast one element from Groups 2 to 15 of the long-form periodic table.For example, M3 is at least one of Co, Mn, Fe, Ni, Mg, Al, B, Ti, V, Nb,Cu, Zn, Mo, Ca, Sr, W, and Zr. Specific examples of the Li complexphosphate having an olivine structure include LiFePO₄, LiCoPO₄,LiFe_(1−p)M31PO₄, LiFe_(1−p−q)M31_(p)M32_(q)PO₄, LiCo_(1−p)M31_(p)PO₄,and LiMn_(1−p)M31_(p)PO₄. Note that M31 represents the same elementsrepresented by M3 (excluding the redundant elements), and p and qsatisfy 0<p<1, and 0<q<1.

Examples of the Li complex phosphate of some other structure includeLi₂Fe₂PO₄ and LiVOPO₄. These Li complex phosphates may further contain asmall amount of at least one of the candidate elements M3 above.

The positive electrode active material is preferably a Li complexoxoacid salt having an olivine structure. The Li complex oxoacid salthaving an olivine structure is preferred, because it has lowerelectrical conductivity than Li complex oxides of a laminar rock saltstructure, and can thus provide higher effects.

(B) Second Condition

The positive electrode active material includes a plurality of primaryparticles. The primary particles have three median diameters D10, D50,and D90 (nm) of the ranges 1 nm<D10<65 nm, 5 nm<D50<75 nm, and 50nm<D90<100 nm as specified from the particle size distribution of theprimary particles. Because the primary particle size is very small anduniform, the ion conduction distance in the primary particles becomesvery short in a uniform fashion. This greatly reduces the lithium iontransfer resistance in the primary particles.

Specifically, when D10 and D90 are outside of the foregoing ranges, theprimary particle size distribution becomes too wide, and the resistancetends to greatly increase mainly in the late stage of repeated chargeand discharge. When D50 is 10 nm or less, the crystallinity of thepositive electrode active material lowers. When D50 is 75 nm or more,the lithium ion diffusion distance in the primary particles becomes toolong. In either case, the ion conductivity tends to decrease.

The median diameter can be examined by, for example, observing thepositive electrode active material (a plurality of primary particles)with a field emission scanning electron microscope (FE-SEM) or the like,and measuring the particle size of each primary particle and theparticle size distribution from the observed image. The median diameter(D10, D50, D90) can then be calculated from the measurement result(particle size distribution). In this case, in order to improve thestatistical reliability, it is preferable to measure the major axis ofeach primary particle as the particle size, and to measure the particlesize for at least 300 primary particles.

In handing the positive electrode active material of a powder form forthe measurement of the median diameter, the primary particles tend tonaturally agglomerate (form secondary particles). However, the particlesize can still be measured for primary particles forming the secondaryparticles, because microscopic observation of the positive electrodeactive material allows the boundaries (contours) of the primaryparticles to be specified in the secondary particles.

When the positive electrode active material in the positive electrode 21exists as a mixture with other materials such as a positive electrodebinder and a positive electrode conductive agent, the positive electrodeactive material may be distinguished from the other materials by elementmapping using, for example, energy dispersive X-ray spectrometry (EDX).The other materials may be simply removed to separate only the positiveelectrode active material.

(C) Third Condition

The positive electrode active material has a plurality of pores betweenthe primary particles. The pores are gaps that generate as a result ofthe primary particles forming the agglomerates (secondary particles).The maximum peak pore size A (nm) as measured from the pore sizedistribution using the mercury intrusion technique is 10 nm≦A≦75 nm.There is a correlation between the pore size and the particle size ofthe primary particles. Thus, the lithium ion diffusion distance in theprimary particles becomes short when the range of the maximum peak poresize A (10 nm to 75 nm) substantially coincides with the main mediandiameter range (5 nm<D50<75 nm). Further, the positive electrode activematerial can easily have high crystallinity in this way.

The pore size distribution may be examined using the mercury intrusiontechnique, for example, by measuring the amount of mercury intruding thepores in the positive electrode active material using a mercuryporosimeter (Shimadzu Corporation; Autopore IV900), and finding therelationship between the intrusion amount of the mercury and the poresize. In the mercury intrusion technique, the mercury intrusion amount Vfor the pores is measured under gradually increasing pressure P, and therate of change of the mercury intrusion amount V with respect topressure P (ΔV/ΔP) is plotted against the pore size. The intrusionamount of mercury herein is a value obtained by approximating thepressure vs. pore size relationship to “180/pressure=pore size” underthe following conditions: mercury surface tension=485 mN/m, mercurycontact angle=130°, measurement temperature=19° C. The pore size Acorresponding to the peak position (apex) can be specified by specifyinga peak (maximum peak) of the maximum intensity from one or more peaksappearing in the mercury porosimeter measurement result (graph).

The number of peaks detected by mercury porosimeter is not particularlylimited. However, it is preferable that one or more peaks appear in thepore size range of 10 nm to 150 nm, depending on the range of the mediandiameter (D10, D50, D90).

As mentioned above, the primary particles of the positive electrodeactive material tend to naturally form secondary particles during thehandling procedure. The pore size distribution can thus be measured byanalyzing the secondary particles using a mercury porosimeter.

(D) Fourth Condition

The ratio B/A of the maximum peak pore size A (nm) and the crystallitesize B (nm) determined from the half width of the X-ray diffractionpattern of the positive electrode active material as measured by X-raydiffractometry (XRD) is 0.5<B/A≦1. In this way, the positive electrodeactive material can have high crystallinity, and the lithium iondiffusion rate increases. The ratio B/A represents the number ofcrystallite domains in the primary particles, and can be used as anindex of the crystallinity of the positive electrode active material.

The crystallite size B is found, for example, by first obtaining anX-ray diffraction pattern through the analysis of the positive electrodeactive material with a X-ray diffractometer (Rigaku Corporation;RINT-2000). Then, four peaks are selected in a descending order of peakintensity from a plurality of peaks detected in the diffraction angle 20range of 15° to 45°. The crystallite size can then be calculated fromthe mean value of the half widths using the Scherrer's equation.

When using the positive electrode active material, it is preferable thatthe direct current resistivity in the charged state with 80% chargedepth be 7.5 kΩ·cm or less. In this way, the constant current state canstays longer in the constant current-constant voltage charging process,and the positive electrode active material can rapidly store and releasethe lithium ions.

It is particularly preferable that the positive electrode activematerial have a carbon material-containing coating on at least a part ofthe primary particle surface. In this way, the resistance of thepositive electrode active material lowers, and the electricalconductivity and ion conductivity improve.

The Raman spectrum of the coating measured by Raman spectroscopy can beused as an index of the extent of the carbonization of the coating(electrical conductivity). It is thus preferable that there is anintensity ratio (I_(D)/I_(G)) of 0.65 or more between the peak obtainedin the 1,250 cm⁻¹ to 1,350 cm⁻¹ range (intensity I_(D)) and the peakobtained in the 1,500 cm⁻¹ to 1,700 cm⁻¹ range (intensity I_(G)). Inthis way, the extent of the coating carbonization increases, andexcellent electrical conductivity can be obtained. Note that a Ramanspectrometer (Renishaw; SYSTEM 2000) is used for the Raman spectrometry.The weight ratio of the coating for the primary particles is notparticularly limited, and is preferably 0.01 weight % to 10 weight %. Inthis way, the resistance of the positive electrode active material canbe further lowered while preventing the storage and release of lithiumions from being suppressed.

The coating may be formed by, for example, dispersing an active materialpowder (a plurality of primary particles) in a solvent with a carbonpowder such as Ketjen black, or with an organic material, such asmaltose, that can be a carbon source, and spraying the resulting liquidin a high-temperature atmosphere by using a method such as spray drying.The solvent may be an organic solvent or water. Because the organicsolvent vaporizes while being sprayed, the primary particle surface isat least partially coated with the carbon material. Here, because theprimary particles agglomerate, there are cases where granules (secondaryparticles) are formed. When obtaining secondary particles using thismethod, for example, the organic solvent temperature and othergranulation conditions may be adjusted to control conditions such as themaximum peak pore size A.

The positive electrode active material layer 21B may include otherpositive electrode active materials, in addition to the positiveelectrode active material satisfying the foregoing four conditions.Examples of such other positive electrode materials include oxides,disulfides, chalcogenides, and conductive polymers. Examples of oxidesinclude titanium oxide, vanadium oxide, and manganese dioxide. Examplesof disulfides include titanium disulfide and molybdenum sulfide.Examples of chalcogenides include niobium selenide. Examples ofconductive polymers include sulfur, polyaniline, and polythiophene.

The positive electrode binder is, for example, one or more syntheticrubbers or polymer materials. Examples of synthetic rubbers includestyrene-butadiene rubbers, fluorine rubbers, and ethylene propylenediene. Examples of polymer materials include polyvinylidene fluoride andpolyimides.

The positive electrode conductive agent is, for example, one or morecarbon materials. Examples of carbon materials include graphite, carbonblack, acetylene black, Ketjenblack, and fibrous carbon. The positiveelectrode conductive agent may be, for example, metallic material orconductive polymer, as long as it has conductivity.

Preferably, the positive electrode conductive agent is fibrous carbon.In this way, because of the fewer contact points in the positiveelectrode conductive agent, a less amount of the positive electrodebinder is needed, and the conductivity mainly along the thickness of thepositive electrode active material layer 21B can improve. The averagefiber diameter of the fibrous carbon is, for example, 1 nm to 200 nm,preferably 10 nm to 200 nm. The aspect ratio (average fiberlength/average fiber diameter) of the fibrous carbon is, for example, 20to 20,000, preferably 20 to 4,000, more preferably 20 to 2,000.

Further, the positive electrode conductive agent, when used for apositive electrode active material layer 21B of an increased thicknessfor improved secondary battery volume efficiency, is preferablysecondary particles of carbon black. This is because the major axis ofthe secondary particles of carbon black is longer than the major axis ofthe fibrous carbon. In this way, as mentioned above, the positiveelectrode binder can be used in smaller amounts, and the conductivity ofthe positive electrode active material layer 21B can improve.

[Negative Electrode]

The negative electrode 22 is structured to include, for example, anegative electrode active material layer 22B provided on at least oneside of a negative electrode collector 22A.

The negative electrode collector 22A is formed of conductive material,for example, such as Cu, Ni, and stainless steel. Preferably, thesurface of the negative electrode collector 22A is roughened. In thisway, the adhesion of the negative electrode active material layer 22Bfor the negative electrode collector 22A can improve by the anchoreffect. In this case, the surface of the negative electrode collector22A may be roughed in at least a region facing the negative electrodeactive material layer 22B. For example, a method that forms fineparticles by electrolysis treatment may be used as the roughing method.The electrolysis treatment is a method by which fine particles areformed on the surface of the negative electrode collector 22A to provideirregularities by electrolysis in an electrolysis vessel. The Cu foilformed by electrolysis is generally called an electrolytic Cu foil.

The negative electrode active material layer 22B includes one or morenegative electrode active materials capable of storing and releasinglithium ions. Other materials such as a negative electrode binder and anegative electrode conductive agent also may be contained, as required.Note that details of the negative electrode binder and the negativeelectrode conductive agent are as described above, for example, inconjunction with the positive electrode binder and the positiveelectrode conductive agent. In order to prevent, for example, accidentaldeposition of Li metal during the charge and discharge, it is preferablein the negative electrode active material layer 22B that the negativeelectrode active material have greater chargeable capacity compared tothe discharge capacity of the positive electrode 21.

The negative electrode active material is an active material for lithiumion secondary batteries of the embodiment of the present technology, andthe negative electrode 22 containing the negative electrode activematerial is an electrode for lithium ion secondary batteries of theembodiment of the present technology. The negative electrode activematerial has the same configuration as the positive electrode activematerial, and satisfies the four conditions. With regard to the firstcondition, the negative electrode active material is a compound (Licomplex oxide) having, for example, a spinel structure, and representedby the formulae (4) to (6) below. Li complex oxides containing Li and Tias constituting elements are more electrochemically stable (lessreactive) than carbon materials (for example, graphite), and thussuppress the degradation reaction of the electrolytic solution due tothe reactivity of the negative electrode 22. The resistance of thenegative electrode 22 thus does not easily increase even after therepeated charge and discharge.

Li[Li_(x)M4_((1−3x)/2)Ti_((3+x)/2)]O₄  (4)

(where M4 is at least one of Mg, Ca, Cu, Zn, and Sr, and x satisfies0≦x≦⅓)

Li[Li_(y)M5_(1−3y)Ti_(1+2y)]O₄  (5)

(where M5 is at least one of Al, Sc, Cr, Mn, Fe, Ga, and Y, and ysatisfies 0≦y≦⅓)

Li[Li_(1/3)M6_(z)Ti_((5/3)−z)]O₄  (6)

(where M6 is at least one of V, Zr, and Nb, and z satisfies 0≦z≦⅔)

The M4 in equation (4) is a metallic element that can be a divalent ion.The M5 in equation (5) is a metallic element that can be a trivalention. The M6 in equation (6) is a metallic element that can be atetravalent ion. Specific examples of the Li complex oxides of equation(1) include Li_(3.75)Ti_(4.875)Mg_(0.375)O₁₂. Specific examples of theLiTi complex oxides of equation (2) include LiCrTiO₄. Specific examplesof the LiTi complex oxides of equation (3) include Li₄Ti₅O₁₂ andLi₄Ti_(4.95)Nb_(0.05)O₁₂.

At least part of the surface of the negative electrode active materialmay be coated with a carbon material-containing coating. In this way,the resistance of the negative electrode active material lowers. Thecoating may be formed by, for example, decomposing hydrocarbons or thelike by using a method such as chemical vapor deposition (CVD), andallowing a carbon coating to grow on the Ti complex oxide surface.

The negative electrode active material layer 22B may also contain othernegative electrode active materials, in addition to the negativeelectrode active materials satisfying the foregoing four conditions.Carbon material is an example of such other negative electrodematerials. Carbon materials undergo very little change in thecrystalline structure during the storage and release of lithium ions,and can thus provide high energy density and excellent cyclecharacteristics. Carbon materials also function as a negative electrodeconductive agent. Examples of carbon material include an easilygraphitizable carbon, a non-graphitizable carbon having a (002) planedistance of 0.37 nm or more, and a graphite having a (002) planedistance of 0.34 nm or less. Specific examples include pyrolyzedcarbons, cokes, glass-like carbon fibers, organic polymer compoundcalcined products, activated carbons, and carbon blacks. Cokes includepitch cokes, needle cokes, and petroleum cokes. The organic polymercompound calcined products refer to products obtained by calcining(carbonizing) polymer compounds such as phenol resin and furan resin atappropriate temperatures. Further, the carbon material may be a lowcrystalline carbon or an amorphous carbon heat-treated at about 1,000°C. or less. The carbon material may be fibrous, spherical, granular, orscale-like in shape.

Other negative electrode active materials are, for example, (metallic)materials that include one or more metallic elements and semi-metallicelements as constituting elements. In this way, high energy density canbe obtained. Note that materials that correspond to the Li complexoxides or the like are excluded. The metallic material may include oneor more metallic elements or semi-metallic elements, either alone or asan alloy or a compound, or may at least partially include one or morephases of these. As used herein, the “alloy” encompasses materialsformed of two or more metallic elements, and materials formed of one ormore metallic elements and one or more semi-metallic elements. Further,the “alloy” may include a non-metallic element. The structure may be asolid solution, a eutectic (eutectic mixture), or an intermetalliccompound, or a mixture of two or more of these.

The metallic and semi-metallic elements are, for example, those capableof forming an alloy with lithium. Specific examples include one or moreof Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Bi, Cd, Ag, Zn, Hf, Zr, Y, Pd, andPt. At least one of Si and Sn is particularly preferred, because theseelements excel in storing and releasing lithium ions, and can thusprovide high energy density.

Examples of materials that include at least one of Si and Sn include oneor more kinds of the elementary substance, alloys and compounds ofsilicon, one or more kinds of the elementary substance, alloys andcompounds of tin, and materials that at least partially include one ormore phases of these. Note that the term “elementary substance” as usedherein is intended to have a general meaning (allows for inclusion oftrace amounts of impurities), and does not necessarily mean 100% purity.

Examples of the silicon alloy include materials including at least onenon-silicon constituting element selected from Sn, Ni, Cu, Fe, Co, Mn,Zn, In, Ag, Ti, Ge, Bi, Sb, and Cr. Examples of the silicon compoundinclude those containing carbon or oxygen as a non-silicon constitutingelement. For example, one or more of the elements presented inconjunction with the silicon alloy may be contained in the siliconcompound as non-silicon constituting elements.

Examples of the silicon alloy or compound include SiB₄, SiB₆, Mg₂Si,Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂, MnSi₂,NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄, Si₂N₂O, SiO_(v) (0<v≦2),and LiSiO. Note that v in SiO_(v) may satisfy 0.2<v<1.4.

Examples of the tin alloy include materials including at least onenon-tin constituting element selected from Si, Ni, Cu, Fe, Co, Mn, Zn,In, Ag, Ti, Ge, Bi, Sb, and Cr. Examples of the tin compound includematerials that contain C or O as a constituting element. For example,one or more of the elements presented in conjunction with the tin alloymay be contained in the tin compound as non-tin constituting elements.Examples of the tin alloy or compound include SnO_(w) (0<w≦2), SnSiO₃,LiSnO, and Mg₂Sn.

Examples of the Sn-containing material include materials that containsecond and third constituting elements in addition to the firstconstituting element tin. Examples of the second constituting elementinclude one or more elements selected from Co, Fe, Mg, Ti, V, Cr, Mn,Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Ce, Hf, Ta, W, Bi, and Si. Examplesof the third constituting element include one or more of B, C, Al, andP. Inclusion of the second and third constituting elements improvesbattery characteristics, including battery capacity and cyclecharacteristics.

Materials containing Sn, Co, and C (SnCoC-containing materials) arepreferred. The composition of the SnCoC-containing material is, forexample, 9.9 mass % to 29.7 mass % carbon, and 20 mass % to 70 mass %Co/(Sn+Co). High energy density can be obtained with these compositionranges.

It is preferable that the SnCoC-containing material include a Sn-, Co-,and C-containing phase, and that this phase is low-crystalline oramorphous. This phase is a reaction phase reactive to lithium, and thepresence of this reaction phase provides excellent characteristics. Thehalf width of the diffraction peak obtained by the X-ray diffractionanalysis of the phase is preferably 1.0° or more in terms of adiffraction angle 2θ, as measured with CuKα rays used as specific X-raysand at a sweep rate of 1°/min. In this way, the lithium ions are moresmoothly stored and released, and the reactivity for the electrolyticsolution weakens. Note that the SnCoC-containing material may alsoinclude the whole or partial phase of each constituting element, inaddition to the low crystalline or amorphous phase.

Whether the diffraction peak obtained by X-ray diffraction correspondsto the reaction phase reactive to lithium can easily be determined bycomparing the X-ray diffraction charts before and after theelectrochemical reaction with lithium. For example, the diffraction peakcorresponds to the reaction phase reactive to lithium when there is achange in the diffraction peak position before and after theelectrochemical reaction with lithium. In this case, for example, thediffraction peak of the low crystalline or amorphous reaction phaseoccurs at 2θ of 20° to 50°. It is considered that such a reaction phaseincludes, for example, the foregoing constituting elements, and mainlyexists as a low crystalline or amorphous phase by the presence ofcarbon.

In the SnCoC-containing material, it is preferable that the constitutingelement carbon at least partially bind to the other constitutingelements, namely, the metallic elements or semi-metallic elements.Bonding of the carbon with other elements suppresses agglomeration orcrystallization of tin or other elements. The state of element bindingcan be measured by, for example, X-ray photoelectron spectroscopy (XPS).Commercially available devices use, for example, Al—Kα rays or Mg—Kαrays as soft X-rays. When the carbon is at least partially binding tothe metallic elements or semi-metallic elements, the peak of the carbonis orbital (C1s) synthetic wave occurs in a region below 284.5 eV. Here,the device is calibrated so that a peak of the gold atom 4f orbital(Au4f) occurs at 84.0 eV. Further, because the surface of a substance istypically contaminated with carbon, the C1s peak of suchsurface-contaminating carbon at 284.8 eV is taken as the referenceenergy. In XPS measurement, because the waveform of the C1s peak isobtained as the waveform that includes the peak of thesurface-contaminating carbon and the peak of the carbon contained in theSnCoC-containing material, these peaks are analyzed and separated byusing, for example, commercially available software. In the waveformanalysis, the position of the main peak on the lowest binding energyside is used as the reference energy (284.8 eV).

The SnCoC-containing material may further contain other constitutingelements, as required. Examples of such other constituting elementsinclude one or more of Si, Fe, Ni, Cr, In, Nb, Ge, Ti, Mo, Al, P, Ga,and Bi.

Aside from the SnCoC-containing material, materials containing Sn, Co,Fe, and C (SnCoFeC-containing materials) are also preferred. TheSnCoFeC-containing materials may have any compositions. For example, acomposition with a low Fe content is 9.9 mass % to 29.7 mass % carbon,0.3 mass % to 5.9 mass % iron, and 30 mass % to 70 mass % (Co/(Sn+Co).Further, for example, a composition with a high Fe content is 11.9 mass% to 29.7 mass % carbon, 26.4 mass % to 48.5 mass % (Co+Fe)/(Sn+Co+Fe),and 9.9 mass % to 79.5 mass % (Co/(Co+Fe). High energy density can beobtained with these composition ranges. The SnCoFeC-containing materialhas the same physical properties (including half width) as theSnCoC-containing material.

Other negative electrode active materials may be, for example, metaloxides or polymer compounds. Examples of metal oxides include ironoxide, ruthenium oxide, and molybdenum oxide. Examples of polymercompounds include polyacetylene, polyaniline, and polypyrrole.

The negative electrode active material layer 22B is formed using, forexample, any of a coating method, a vapor-phase method, a liquid-phasemethod, a spray method, and a calcining method (sinter method), eitherindividually or in combinations of two or more. The coating method is amethod whereby, for example, a powdery negative electrode activematerial is mixed with a binder and the like, and dispersed in anorganic solvent or the like for coating. The vapor-phase method may be,for example, a physical deposition method or a chemical depositionmethod, specifically, a vacuum deposition method, a sputter method, anion plating method, a laser abrasion method, a thermal chemical vapordeposition, a chemical vapor deposition (CVD) method, or a plasmachemical vapor deposition method. The liquid-phase method may be, forexample, an electrolytic plating method, or a non-electrolytic platingmethod. The spray method is a method by which the negative electrodeactive material is sprayed in the molten state or semi-molten state. Thecalcining method is, for example, a method involving a heat treatment ata temperature higher than the melting point of the binder or the likeafter the coating is formed by the same procedure used in the coatingmethod. Known techniques may be used for the calcining method. Examplesinclude an atmospheric calcining method, a reactive calcining method,and a hot-press calcining method.

In the lithium ion secondary battery, as described above, the negativeelectrode material capable of storing and releasing lithium ions has agreater electrochemical equivalent than the positive electrode, in orderto prevent accidental deposition of the lithium metal on the negativeelectrode 22 during the charging process. Further, because the amount ofreleased lithium ions per unit mass increases when the fully chargedopen circuit voltage (i.e., battery voltage) is 4.25 V or more than when4.20 V even with the same positive electrode active material, theamounts of the positive electrode active material and the negativeelectrode active material are adjusted taking this into account. In thisway, high energy density can be obtained.

Even though the positive electrode 21 and the negative electrode 22 havebeen described as containing active material that satisfies theforegoing four conditions, only one of the positive electrode 21 and thenegative electrode 22 may contain such active material.

[Separator]

The separator 23 is provided to isolate the positive electrode 21 andthe negative electrode 22 from each other, and allows for passage oflithium ions while preventing current shorting caused by contacting ofthe electrodes. The separator 23 is configured using, for example, aporous film of synthetic resin or ceramic. The separator 23 may be alaminate of two or more of such porous films. Examples of the syntheticresin include polytetraf luoroethylene, polypropylene, and polyethylene.

[Electrolytic Solution]

The separator 23 is impregnated with a liquid electrolyte, electrolyticsolution. The electrolytic solution is a solution of an electrolyte saltdissolved in a solvent, and may contain other materials such asadditives, as required.

The solvent includes one or more nonaqueous solvents such as organicsolvents. Examples include ethylene carbonate, propylene carbonate,butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methylcarbonate, methyl propyl carbonate, γ-butyrolactone, γ-valerolactone,1,2-dimethoxyethane, and tetrahydrofuran. Other examples include2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolan,4-methyl-1,3-dioxolan, 1,3-dioxane, and 1,4-dioxane. Yet other examplesinclude methyl acetate, ethyl acetate, methyl propionate, ethylpropionate, methyl butyrate, methyl isobutyrate, methyltrimethylacetate, and ethyl trimethylacetate. Still other examplesinclude acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile,3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidinone,and N-methyloxazolidinone. Yet other examples include N,N′-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethylphosphate, and dimethyl sulfoxide. Use of these solvents improvesbattery characteristics, including battery capacity, cyclecharacteristics, and storage characteristics.

At least one of ethylene carbonate, propylene carbonate, dimethylcarbonate, diethyl carbonate, and ethyl methyl carbonate areparticularly preferred, because these provide superior characteristics.In this case, it is preferable to use a high-viscosity (high-dielectric)solvent (for example, relative permittivity ∈≧30), for example, such asethylene carbonate and propylene carbonate, as a mixture with alow-viscosity solvent (for example, viscosity 1≦mPa·s), for example,such as dimethyl carbonate, ethyl methyl carbonate, and diethylcarbonate. The use of such mixtures improves the dissociation of theelectrolyte salt and ion mobility.

It is particularly preferable that the solvent contain an unsaturatedcarbon bond cyclic carbonate ester. In this way, a stable protectivefilm forms on the surface of the negative electrode 22 during the chargeand discharge, and suppresses the degradation reaction of theelectrolytic solution. The unsaturated carbon bond cyclic carbonateester is a cyclic carbonate ester having one or more unsaturated carbonbonds. Examples include vinylene carbonate and vinyl ethylene carbonate.The content of the unsaturated carbon bond cyclic carbonate ester in thesolvent is not particularly limited, and is, for example, 0.01 weight to10 weight %. In this way, the degradation reaction of the electrolyticsolution can be suppressed without excessively lowering batterycapacity.

It is preferable that the solvent contain at least one of a halogenatedchain carbonate ester and a halogenated cyclic carbonate ester. In thisway, a stable protective film forms on the surface of the negativeelectrode 22 during the charge and discharge, and suppresses thedegradation reaction of the electrolytic solution. The halogenated chaincarbonate ester is a chain carbonate ester having one or more halogengroups. The halogenated cyclic carbonate ester is a cyclic carbonateester having one or more halogen groups. The halogen groups are notparticularly limited, and are preferably fluorine group, chlorine group,or bromine group, of which the fluorine group is more preferred. In thisway, high effects can be obtained. The number of halogen groups ispreferably two, rather than one, and may be three or more. In this way,a stronger and more stable protective film forms, and suppresses thedegradation reaction of the electrolytic solution more effectively.Examples of the halogenated chain carbonate ester include fluoromethylmethyl carbonate, bis(fluoromethyl)carbonate, and difluoromethyl methylcarbonate. Examples of the halogenated cyclic carbonate ester include4-fluoro-1,3-dioxolan-2-one, and 4,5-difluoro-1,3-dioxolan-2-one. Thecontents of the halogenated chain carbonate ester and halogenated cycliccarbonate ester in the solvent are not particularly limited, and are,for example, 0.01 weight to 50 weight %. In this way, the degradationreaction of the electrolytic solution can be suppressed without loweringbattery capacity.

The solvent may also contain sultone (cyclic sulfonic acid ester). Thisimproves the chemical stability of the electrolytic solution. Examplesof sultone include propane sultone, and propene sultone. The sultonecontent in the solvent is not particularly limited, and is, for example,0.5 weight % to 5 weight %. In this way, the degradation reaction of theelectrolytic solution can be suppressed without excessively loweringbattery capacity.

The solvent may further contain acid anhydrides. This improves thechemical stability of the electrolytic solution. Examples of acidanhydrides include dicarboxylic acid anhydrides, disulfonic acidanhydrides, and carboxylic acid sulfonic acid anhydrides. Examples ofdicarboxylic acid anhydrides include succinic acid anhydride, glutaricacid anhydride, and maleic acid anhydride. Examples of disulfonic acidanhydrides include ethanedisulfonic acid anhydride, andpropanedisulfonic acid anhydride. Examples of carboxylic acid sulfonicacid anhydrides include sulfobenzoic acid anhydride, sulfopropionic acidanhydride, and sulfobutyric acid anhydride. The acid anhydride contentin the solvent is not particularly limited, and is, for example, 0.5weight % to 5 weight %. In this way, the degradation reaction of theelectrolytic solution can be suppressed without excessively loweringbattery capacity.

[Electrolyte Salt]

The electrolyte salt includes, for example, one or more lithium salts,as follows. The electrolyte salts may be salts other than lithium salts(for example, light metal salts other than lithium salts).

The lithium salts may be, for example, compounds such as LiPF₆, LiBF₄,LiClO₄, LiAsF₆, LiB(C₆H₅)₄, LiCH₃SO₃, LiCF₃SO₃, LiAlCl₄, Li₂SiF₆, LiCl,and LiBr. These compounds can improve battery characteristics, includingbattery capacity, cycle characteristics, and storage characteristics. Atleast one of LiPF₆, LiBF₄, LiClO₄, and LiAsF₆ is preferred, and LiPF₆ isparticularly preferred, because these lowers the internal resistance andprovide higher effects.

The electrolyte salt content is preferably from 0.3 mol/kg to 3.0 mol/kgwith respect to the solvent, because it provides high ion conductivity.

[Operation of Secondary Battery]

In the secondary battery, for example, the lithium ions released fromthe positive electrode 21 while charging are stored in the negativeelectrode 22 via the electrolytic solution. During the discharge, forexample, the lithium ions released from the negative electrode 22 arestored in the positive electrode 21 via the electrolytic solution.

[Secondary Battery Producing Method]

The secondary battery is produced, for example, according to thefollowing procedures.

The positive electrode 21 is fabricated by first mixing the positiveelectrode active material satisfying the foregoing four conditions withoptional materials such as a positive electrode binder and a positiveelectrode conductive agent to provide a positive electrode mixture. Thepositive electrode mixture is then dispersed in an organic solvent orthe like to obtain a paste-like positive electrode mixture slurry. Thepositive electrode mixture slurry is applied on the both sides of thepositive electrode collector 21A, and dried to form the positiveelectrode active material layer 21B. Finally, the electrode activematerial layer 21B is compression-molded with a roller press machine orthe like while being heated, as required. The compression molding may berepeated more than once.

The negative electrode 22 is fabricated using the same procedure usedfor the positive electrode 21. Specifically, the negative electrodeactive material satisfying the foregoing four conditions is mixed withoptional materials such as a negative electrode binder and a negativeelectrode conductive agent to provide a negative electrode mixture,which is then dispersed in an organic solvent or the like to obtain apaste-like negative electrode mixture slurry. The negative electrodemixture slurry is then applied to the both sides of the negativeelectrode collector 22A, and dried to form the negative electrode activematerial layer 22B. The negative electrode active material layer 22B isthen compression-molded, as required.

The secondary battery is assembled by first attaching the positiveelectrode lead 25 to the positive electrode collector 21A, and thenegative electrode lead 26 to the negative electrode collector 22A, byusing a method such as welding. The positive electrode 21 and thenegative electrode 22 are then laminated with the separator 23interposed in between and wound together to fabricate the woundelectrode unit 20. The center pin 24 is inserted at the center of thewound electrode unit 20. Thereafter, the wound electrode unit 20 whichis interposed between the insulating plates 12 and 13 is housed insidethe battery canister 11. Here, the positive electrode lead 25 and thenegative electrode lead 26 are attached to the safety valve mechanism 15and the battery canister 11, respectively, at the leading ends, using amethod such as welding. Then, the electrolytic solution is injected intothe battery canister 11 to impregnate the separator 23 with theelectrolytic solution. Finally, the battery lid 14, the safety valvemechanism 15, and the heat-sensitive resistive element 16 are swaged tothe open end of the battery canister 11 via the gasket 17.

Note that the secondary battery completed this way may be disassembledto take out the positive electrode 21 (positive electrode activematerial layer 21B) and the negative electrode 22 (negative electrodeactive material layer 22B) for observation and measurement with amicroscope. In this way, the four conditions, particularly the particlesize distribution of the primary particles, and the pore sizedistribution can be measured post fabrication. This is possible becausethe original particle size of the primary particles, and the state ofthe secondary particles are maintained even after the completion of thesecondary battery. In this case, materials such as the positiveelectrode binder may be dissolved and removed using an organic solventor the like, or the unnecessary solvent components (the electrolyticsolution, etc.) may be vaporized by heating, as required. The particlesize distribution and the pore size distribution are maintained evenafter the secondary battery is used (charged and discharged), becausethese characteristics are hardly affected by the charge and discharge.

[Advantages of Secondary Battery]

The positive electrode active material of the positive electrode 21, andthe negative electrode active material of the negative electrode 22 ofthe cylindrical secondary battery satisfy the foregoing four conditions(A) to (D). This makes the diameter of the primary particles uniform andsmall, and thus reduces the diffusion distance of the lithium ions inthe primary particles. Further, because of high crystallinity, thediffusion rate of the lithium ions in the primary particles increases.This suppresses the overvoltage at the late stage of charging ordischarge, and improves the input-output characteristics of lithiumions. This makes it possible to suppress the accidental deposition ofthe lithium metal as might occur, for example, in the process ofhigh-speed charging or low-temperature charging.

Higher effects can be obtained with the carbon material-containingcoating formed on at least a part of the primary particle surface,because such a coating improves the electrical conductivity and ionconductivity. Here, even higher effects can be obtained when theintensity ratio I_(D)/I_(G) of the peaks measured by Raman spectroscopyis 0.65 or more, because it improves the extent of carbonization.Effects can be even more improved when the weight ratio of the coatingwith respect to the primary particles is from 0.01 weight % to 10 weight%.

Note that the positive electrode 21 and the negative electrode 22 weredescribed as containing the active materials (positive electrode activematerial and negative electrode active material, respectively)satisfying the foregoing four conditions. However, only one of thepositive electrode 21 and the negative electrode 22 may contain theactive material satisfying the four conditions. The same effect can beobtained in this case.

<1-2. Laminate Film Secondary Battery>

FIG. 3 is an exploded perspective view of another lithium ion secondarybattery according to the embodiment of the present technology. FIG. 4 isa magnified cross sectional view of a wound electrode unit 30illustrated in FIG. 3, taken along the line IV-IV. In the following, theconstituting elements of the cylindrical lithium ion secondary batterydescribed above will be referred to as needed.

[Overall Configuration of Secondary Battery]

The secondary battery described here is so-called a laminate filmsecondary battery. The secondary battery includes the wound electrodeunit 30 housed in a film-like exterior member 40. The wound electrodeunit 30 includes a positive electrode 33 and a negative electrode 34laminated with a separator 35 and an electrolyte layer 36 interposed inbetween and wound together. A positive electrode lead 31 and a negativeelectrode lead 32 are attached to the positive electrode 33 and thenegative electrode 34, respectively. The outermost periphery of thewound electrode unit 30 is protected by a protective tape 37.

For example, the positive electrode lead 31 and the negative electrodelead 32 lead out in the same direction out of the exterior member 40.The positive electrode lead 31 is formed using, for example, conductivematerial such as aluminum. The negative electrode lead 32 is formedusing, for example, conductive material such as copper, nickel, andstainless steel. These materials are formed into, for example, a thinplate or a mesh.

The exterior member 40 is, for example, a laminate film that includes afuse layer, a metal layer, and a surface protective layer laminated inthis order. For example, two laminate films are bonded to each other bybeing fused or with an adhesive or the like at the peripheries of theopposing fuse layers of the laminate films so that the fuse layers facethe wound electrode unit 30. The fuse layer is, for example, apolyethylene film or a polypropylene film. The metal layer is, forexample, an aluminum foil. The surface protective layer is, for example,a nylon film or a polyethylene terephthalate film.

The exterior member 40 is preferably an aluminum laminate film thatincludes a polyethylene film, an aluminum foil, and a nylon filmlaminated in this order. However, the exterior member 40 may be alaminate film of some other laminate structure, a polymer film ofpolypropylene or the like, or a metal film.

An adhesive film 41 for preventing entry of ambient air is insertedbetween the exterior member 40 and the positive and negative electrodeleads 31 and 32. The adhesive film 41 is formed of material adherent tothe positive and negative electrode leads 31 and 32. Examples of suchmaterial include polyolefin resins such as polyethylene, polypropylene,modified-polyethylene, and modified-polypropylene.

The positive electrode 33 includes a positive electrode active materiallayer 33B provided, for example, on the both sides of a positiveelectrode collector 33A. The negative electrode 34 includes a negativeelectrode active material layer 34B provided, for example, on the bothsides of a negative electrode collector 34A. The positive electrodecollector 33A, positive electrode active material layer 33B, thenegative electrode collector 34A, and the negative electrode activematerial layer 34B are configured in the same way as the positiveelectrode collector 21A, the positive electrode active material layer21B, the negative electrode collector 22A, and the negative electrodeactive material layer 22B. Accordingly, the positive electrode 33 andthe negative electrode 34 include a positive electrode active materialand a negative electrode active material, respectively, satisfying theforegoing four conditions. The separator 35 is configured in the sameway as the separator 23.

The electrolyte layer 36 contains a polymer compound holding anelectrolytic solution. Other materials such as additives also may becontained, as required. The electrolyte layer 36 is so-called a gelelectrolyte. In this way, high ion conductivity (for example, 1 mS/cm ormore at room temperature) can be obtained, and the electrolytic solutioncan be prevented from leaking.

Examples of the polymer compound include one or more of the polymermaterials selected from polyacrylonitrile, polyvinylidene fluoride,polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide,polypropylene oxide, polyphosphazene, polysiloxane, and polyvinylfluoride. Other examples include polyvinyl acetate, polyvinyl alcohol,polymethylmethacrylate, polyacrylic acid, polymethacrylic acid,styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene,polycarbonate, and a copolymer of vinylidene fluoride andhexafluoropyrene. Of these, polyvinylidene fluoride, and a copolymer ofvinylidene fluoride and hexafluoropyrene are preferred, andpolyvinylidene fluoride is more preferred, because these areelectrochemically stable.

The composition of the electrolytic solution is the same as that for thecylindrical secondary battery. However, in the electrolyte layer 36 asthe gel electrolyte, the nonaqueous solvent of the electrolytic solutionis inclusive of not only liquid solvents, but a wide range of ionconductive materials that can dissociate an electrolyte salt. Thus, apolymer compound having ion conductivity is also within the definitionof the solvent.

Note that the electrolytic solution may directly be used instead of thegel electrolyte layer 36. In this case, the separator 35 is impregnatedwith the electrolytic solution.

[Operation of Secondary Battery]

In the secondary battery, for example, the lithium ions released fromthe positive electrode 33 is stored in the negative electrode 34 via theelectrolyte layer 36 while charging. During the discharge, for example,the lithium ions released from the negative electrode 34 is stored inthe positive electrode 33 via the electrolyte layer 36.

[Secondary Battery Producing Method]

The secondary battery including the gel electrolyte layer 36 is producedby, for example, the following three procedures.

In a first procedure, the positive electrode 33 and the negativeelectrode 34 are fabricated using the same procedure used for thepositive electrode 21 and the negative electrode 22. The positiveelectrode 33 is fabricated by forming the positive electrode activematerial layer 33B on the both sides of the positive electrode collector33A. The negative electrode 34 is fabricated by forming the negativeelectrode active material layer 34B on the both sides of the negativeelectrode collector 34A. In this case, active materials satisfying theforegoing four conditions are used as the positive electrode activematerial and the negative electrode active material, as required.Thereafter, a precursor solution containing an electrolytic solution, apolymer compound, and a solvent such as an organic solvent is prepared,and applied to the positive electrode 33 and the negative electrode 34to form the gel electrolyte layer 36. The positive electrode lead 31 andthe negative electrode lead 32 are then attached to the positiveelectrode collector 33A and the negative electrode collector 34A,respectively, by using a method such as welding. The positive electrode33 and the negative electrode 34 with the electrolyte layer 36 are thenlaminated with the separator 35 interposed in between and wound togetherto fabricate the wound electrode unit 30, and the protective tape 37 isattached to the outermost periphery. The wound electrode unit 30 issandwiched between a pair of film-like exterior members 40, and theouter peripheries of the exterior members 40 are bonded by a method suchas a heat fuse method to seal the wound electrode unit 30. In this case,the adhesive film 41 is inserted between the positive and negativeelectrode leads 31 and 32 and the exterior member 40.

In a second procedure, the positive electrode lead 31 and the negativeelectrode lead 32 are attached to the positive electrode 33 and thenegative electrode 34, respectively. The positive electrode 33 and thenegative electrode 34 are then laminated with the separator 35interposed in between and wound together to fabricate a wound unit as aprecursor of the wound electrode unit 30. The protective tape 37 isattached to the outermost peripheries of the wound unit. The wound unitis then sandwiched between a pair of film-like exterior members 40, andthe all outer peripheries except for one side are bonded by using amethod such as a heat fuse method to house the wound unit inside a bagof the exterior members 40. Then, an electrolyte composition is preparedthat contains an electrolytic solution, the raw material monomer of apolymer compound, a polymerization initiator, and optional materialssuch as a polymerization inhibitor, and injected into the bag of theexterior members 40. The exterior member 40 is then sealed by using amethod such as a heat fuse method, and the monomer is heat polymerized.This forms the polymer compound, and completes the gel electrolyte layer36.

In a third procedure, a wound unit is fabricated and housed in a bag ofthe exterior members 40 in the same manner as in the second procedure,except for using a separator 35 coated with a polymer compound on theboth sides. Examples of the polymer compound applied to the separator 35include polymers that contain a vinylidene fluoride component (includinga homopolymer, a copolymer, and a multicomponent copolymer). Specificexamples include binary copolymers containing polyvinylidene fluoride,vinylidene fluoride, and hexafluoropropylene components, and ternarycopolymers containing vinylidene fluoride, hexafluoropropylene, andchlorotrifluoroethylene components. A polymer containing a vinylidenefluoride component may be used with one or more other polymer compounds.Thereafter, an electrolytic solution is prepared, and injected into theexterior member 40. The opening of the exterior member 40 is then sealedby using a method such as a heat fuse method. The exterior member 40 isthen heated under applied load to bring the separator 35 into contactwith the positive electrode 33 and the negative electrode 34 via thepolymer compound. As a result, the polymer compound is impregnated withthe electrolytic solution, and gelates to form the electrolyte layer 36.

The swelling of the secondary battery is suppressed more in the thirdprocedure than in the first procedure. Further, in the third procedure,the raw material monomer of the polymer compound, the solvent, and othermaterials hardly remain in the electrolyte layer 36 as compared with thesecond procedure, and thus formation of the polymer compound can bedesirably controlled. Thus, sufficient adhesion can be provided betweenthe electrolyte layer 36 and the positive and negative electrodes 33 and34 and the separator 35.

[Advantages of Secondary Battery]

The positive electrode active material of the positive electrode 33, andthe negative electrode active material of the negative electrode 34 ofthe laminate film secondary battery satisfy the foregoing fourconditions. The input-output characteristics of the lithium ions canthus be improved for the same reason described for the cylindricalsecondary battery. Other advantages are as described for the cylindricalsecondary battery.

<2. Use of Lithium Ion Secondary Battery>

Application examples of the lithium ion secondary batteries aredescribed below.

Use of the secondary batteries is not particularly limited, as long asthe secondary batteries are used for machines, devices, equipment,apparatuses, and systems (an assembly of more than one device) that canuse the secondary batteries as driving power supplies, or power storagesources for power accumulation. For use as a power supply, the secondarybattery may be a main power supply (a power supply with a priority), oran auxiliary power supply (a power supply used as a replacement for themain power supply, or a power supply switched from the main powersupply). In the latter, the main power supply is not limited to asecondary battery.

For example, the secondary batteries may be used in electronic devicessuch as video cameras, digital still cameras, mobile phones, laptoppersonal computers, cordless telephones, stereophones, portable radios,portable televisions, and portable information terminals (PDA: personaldigital assistant). Examples of the electronic devices include everydayelectrical appliances such as an electric shaver; storage devices suchas a backup power supply and a memory card; and medical electronicdevices such as a pacemaker and a hearing aid. Other examples includeelectric power tools such as an electric drill and an electric saw. Yetother examples include electric vehicles such as electric automobiles(including hybrid cars). Still other examples include power storagesystems such as a home battery system that accumulates power in case ofemergency.

The secondary batteries are particularly effective for, for example,electronic devices, electric power tools, electric vehicles, and powerstorage systems. Because these applications require excellentcharacteristics for the secondary battery, use of the secondary batteryof the embodiment of the present technology can effectively improvebattery characteristics. Note that the electronic device is one thatexecutes various functions (for example, playing music) using thesecondary battery as the power supply of operation. The electric powertool is one that moves the moving part (for example, a drill), using thesecondary battery as the driving power supply. The electric vehicle isone that runs on the secondary battery as the driving power supply, andmay be an automobile (including hybrid cars) equipped with other drivingsources in addition to the secondary battery. The power storage systemis one that uses the secondary battery as the power storage source. Forexample, in the home power storage system, power is accumulated in thesecondary battery used as the power storage source, and the power storedin the secondary battery is consumed as needed to enable use of varioustypes of devices such as a home electric product.

EXAMPLES

Specific examples of the present technology are described below indetail.

Experiment Examples 1 to 12

Li complex phosphates of an olivine structure were obtained as thepositive electrode active material according to the following procedure.

First, powders of lithium phosphate (Li₃PO₄), manganese(II) phosphatetrihydrate (MnHPO₄.3H₂O), and iron(III) phosphate octahydrate(FePO₄.8H₂O) were weighed and mixed in a total weight of 600 g. Themixture was then charged into deionized water 4 dm³ (=L), and stirred toobtain a slurry. Here, the amount of each powder was adjusted so as tomix Li, Mn, Fe, and P in the molar ratios presented in Table 1. Theslurry was thoroughly stirred after adding 100 g of maltose. Then, theslurry was wet pulverized in the vessel of a bead mill, specifically awet pulverizer-disperser (Ashizawa Finetech Ltd.; DMR/S110). Here, ZrO₂beads were used that had one or more bead sizes (mm) as presented inTable 1, and the mill was run at the rim speed of 12 m/sec for 120 min.The resulting pulverized slurry was dry granulated by spray drying at anintake air temperature of 200° C. to obtain a precursor powder. Finally,the precursor powder was calcined under 1000 N₂ atmosphere at thetemperatures (° C.) and for the durations (min) presented in Table 1 toobtain Li complex phosphates of an olivine structure as primaryparticles.

A series of parameters for the positive electrode active material arepresented in Table 2.

For the measurement of median diameter (D10, D50, D90: nm), the positiveelectrode active material was observed with a FE-SEM (Hitachi; S4300),and the particle sizes (major axis) of 300 primary particles weremeasured from the observed image. Each median diameter was thendetermined from the measurement result (particle size distribution).

The intrusion amount of mercury for the pores was measured with amercury porosimeter (Shimadzu Corporation; Autopore IV900) to examinethe maximum peak pore size A (nm) in the pore size distribution, usingthe mercury intrusion technique. The pore size A at the maximum peakposition was then specified from the measurement result (pore sizedistribution). Crystallite size B (nm) was examined from the X-raydiffraction pattern obtained by analyzing the positive electrode activematerial with an X-ray diffractometer (Rigaku Corporation; RINT-2000).Four peaks were selected in a descending order of peak intensity from aplurality of peaks detected from the X-ray diffraction pattern in thediffraction angle 2θ range of 15° to 45°, and the crystallite size B wascalculated from the mean value of the half widths, using the Scherrer'sequation. The ratio B/A was calculated from these results.

The Raman spectrum of the coating was measured to examine the intensityratio I_(D)/I_(G), using a Raman spectroscope (Renishaw; SYSTEM 2000).The intensity ratio I_(D)/I_(G) of two peaks (a peak with intensityI_(D) in the 1,250 cm⁻¹ to 1,350 cm⁻¹ range, and a peak with intensityI_(G) in the 1,500 cm⁻¹ to 1,700 cm⁻¹ range) was calculated from themeasurement result.

The positive electrode active materials so obtained were used tofabricate coin-shaped secondary batteries (FIG. 5) according to thefollowing procedure.

The coin-shaped secondary battery includes an exterior canister 52 andan exterior cup 55 laminated via a separator 55 impregnated with anelectrolytic solution, and swaged via a gasket 56. A test electrode 51using the positive electrode active material is housed in the exteriorcanister 52, and a counter electrode 53 is attached to the exterior cup54.

The test electrode 51 was fabricated by forming a pellet from a mixtureof the positive electrode active material (a Li complex oxoacid salt ofan olivine structure; 50 parts by mass), and the positive electrodeconductive agent Ketjen black (50 parts by mass). A Li metal plate wasused as the counter electrode 53. The electrolytic solution was preparedby mixing the solvents ethylene carbonate (EC) and dimethyl carbonate(DMC), and dissolving the electrolyte salt LiPF₆. Here, the solvent hadthe composition (mass ratio) EC:DMC=50:50, and the electrolyte saltcontent was 1 mol/dm³ (=1 mol/l) with respect to the solvent. Apolypropylene porous film was used as the separator 55.

Various characteristics of the secondary batteries were examined. Theresults are presented in Table 2.

Resistance characteristic was examined in a charged state at 80% chargedepth by electrochemically inserting the lithium ions in the repeatedcycle of 1C constant-current charging and at least 5 hours ofrelaxation. The direct current resistivity (kΩ·cm) was then determinedby Ohm's law from the voltage difference (the difference between thevoltage immediately before the start of relaxation and the voltage afterthe relaxation) and the current value. Here, for convenience, thecapacity for the 20-hour constant-current constant-voltage charging to aLi metal potential of 4.35 V at 0.1 C current was regarded as the 100%charged state. Note that “1 C” and “0.1 C” are the current values withwhich the theoretical capacity fully discharges in 1 hour and 10 hours,respectively.

Input-output characteristic was examined by measuring the chargecapacity (mAh/g) for the 2.5-hour constant-current constant-voltagecharging to a Li metal potential of 4.35 V at 1 C current. The dischargecapacity (mAh/g) for the 20-hour constant-current constant-voltagecharging to a Li metal potential of 4.35 V at 0.1 C, followed by thedischarge to a Li metal potential 2.0 Vat 3 C current was also measured.Note that “3 C” is the current value with which the theoretical capacityfully discharges in ⅓ hours.

TABLE 1 Positive electrode active material: Li complex phosphate(olivine structure) Experi- Bead Calcine ment Molar ratio diameterTemperature Time example Li Mn Fe P (mm) (° C.) (min) 1 1.00 0.75 0.251.00 0.05 600 180 2 1.00 0.75 0.25 1.00 0.05 650 180 3 1.00 — 1.00 1.000.05 600 180 4 1.00 — 1.00 1.00 0.05 650 180 5 1.00 0.75 0.25 1.00 0.3600 180 6 1.00 0.75 0.25 1.00 0.05 500 180 7 1.00 0.75 0.25 1.00 0.05750 180 8 1.00 0.75 0.25 1.00 0.3 + 0.05 600 180 9 1.00 0.75 0.25 1.000.05 600 5 10 1.00 — 1.00 1.00 0.3 600 180 11 1.00 — 1.00 1.00 0.05 750180 12 1.00 0.75 0.25 1.00 0.3 600 1440

TABLE 2 Positive electrode active material: Li complex phosphate(olivine structure) Median Pore Crystallite DC Charge DischargeExperiment diameter (nm) size A size B Ratio Intensity resistivitycapacity capacity Example D10 D50 D90 (nm) (nm) B/A ratio I_(D)/I_(G)(kΩ · cm) (mAh/g) (mAh/g) 1 48 63 78 45 31 0.69 0.67 6.0 156 147 2 53 7397 46 32 0.70 0.74 6.4 153 152 3 45 58 74 45 41 0.91 0.74 6.5 151 149 458 69 88 51 42 0.82 0.77 6.4 152 148 5 45 60 78 45 30 0.67 0.58 7.0 150140 6 74 95 127 100 37 0.37 0.68 10.9 136 118 7 61 83 108 51 32 0.630.76 8.1 139 80 8 58 72 118 45 34 0.76 0.74 9.3 126 98 9 40 70 85 45 180.40 0.66 12.4 135 105 10 84 102 123 103 45 0.44 0.72 7.9 149 102 11 6495 114 51 47 0.92 0.77 11.7 120 85 12 71 101 132 102 58 0.57 0.71 9.3138 123

The direct current resistivity was lower, and the high-load chargecapacity and discharge capacity were higher when the series ofparameters for the positive electrode active material were all confinedin the appropriate ranges (Experiment Examples 1 to 5) than when theseconditions were not satisfied (Experiment Examples 6 to 12). Theappropriate ranges of these parameters are as follows. Median diameter:1 nm<D10<65 nm, 5 nm<D50<75 nm, and 50 nm<D90<100 nm. Maximum peak poresize A: 10 nm≦A≦75 nm. The ratio B/A of pore size A and crystallite sizeB: 0.5<B/A≦1. The results were particularly desirable when the intensityratio I_(D)/I_(G) was 0.65 or more.

These results indicate the following trends. The particle size andcrystallinity of the primary particles have effects on the storage andrelease of the lithium ions in the positive electrode active material.Specifically, when the particle size of the primary particles isnon-uniform and large, the positive electrode active material cannoteasily store and release the lithium ions, irrespective of thecrystallinity. On the other hand, when the particle size of the primaryparticles is uniform and small, the storage and release of lithium ionsoccurs easily when the crystallinity is high, whereas the storage andrelease of lithium ions becomes difficult at low crystallinity. Thus,the positive electrode active material specifically has low resistance,and high charge capacity and high discharge capacity even under a highload when the primary particles have uniform and small particle sizesand high crystallinity (Experiment Examples 1 to 5).

Experiment Examples 13 and 14

Li complex oxides of a spinel structure were obtained as the negativeelectrode active material according to the following procedure.

Lithium hydroxide monohydrate (LiOH.H₂O) and anatase-type titaniumoxide(IV) (TiO₂) were weighed and mixed at a Li:Ti molar ratio of 4:5 ina total of 600 g. The mixture was charged into deionized water (4 dm³),and stirred to obtain a slurry. After further being stirred thoroughlyin a tank, the slurry was charged into the vessel of the bead mill, andwet pulverized. Here, ZrO₂ beads were used, and the mill was run at arim speed of 12 m/s for 120 min. The ZrO₂ beads had a bead size of 0.05mm (Experiment Example 13) or 0.3 mm (Experiment Example 14). Theresulting pulverized slurry was dry granulated by spray drying at anintake air temperature of 200° C. to obtain a precursor powder. Finally,the precursor powder was calcined in the atmosphere (750° C.×3 hr) toobtain a Li complex oxide. A series of parameters for the negativeelectrode active materials are presented in Table 3.

The input-output characteristics of the lithium ion secondary batteriesusing these negative electrode active materials were examined. Theresults are presented in Table 3. The parameters of the negativeelectrode active materials, the configuration and producing method ofthe secondary batteries, and the measurement conditions of variouscharacteristics are as described in Experiment Examples 1 to 12. Note,however, that the input-output characteristics were examined bymeasuring the charge capacity for the 5-hour constant-currentconstant-voltage charging to a Li metal potential of 1.0 V at 0.5 Ccurrent, followed by charging to a Li metal potential of 2.0 V at 3 C.

TABLE 3 Negative electrode active material: Li complex oxide (spinelstructure) Molar Median Pore Crystallite Charge Discharge Experimentratio diameter (nm) size A size B capacity capacity Example Li Ti D10D50 D90 (nm) (nm) Ratio B/A (mAh/g) (mAh/g) 13 4 5 28 52 90 40 35 0.88173 170 14 4 5 50 97 134 102 45 0.44 162 132

The results obtained for the positive electrode active materials (Table2) were also obtained for the negative electrode active materials.Specifically, the direct current resistivity was lower, and thehigh-load charge capacity and discharge capacity were higher when theseries of parameters for the negative electrode active material were allconfined in the appropriate ranges (Experiment Example 13) than whenthese conditions were not satisfied (Experiment Example 14).

It can be said from the results presented in Tables 1 to 3 that thelithium ion input-output characteristics improve when at least one ofthe positive electrode and the negative electrode contains the activematerial that is capable of storing and releasing lithium ions and thatsatisfies the foregoing four conditions.

While the present technology has been described based on certainembodiments and examples, the present technology is not limited to theforegoing embodiments and examples, and various modifications arepossible. For example, the positive electrode active material of theembodiment of the present technology is also applicable to a lithium ionsecondary battery in which the negative electrode capacity includes thelithium ion storage and release capacity and the capacity associatedwith the deposition and dissolution of the lithium metal, and isrepresented by the sum of these capacities. In this case, the chargeablecapacity of the negative electrode material is made smaller than thepositive electrode discharge capacity.

Further, even though the battery structure was described as beingcylindrical or a laminate film, or the battery element was described ashaving a wound structure in the foregoing embodiments and examples, thepresent technology is not limited to these. The lithium ion secondarybattery of the embodiment of the present technology is also applicableto other battery structures, including coin-shaped, rectangular, andbutton-shaped structures, and to battery elements of other structures,including a laminate structure.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-104266 filed in theJapan Patent Office on Mar. 9, 2011, the entire contents of which arehereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A lithium ion secondary battery comprising: apositive electrode; a negative electrode; and an electrolytic solution,at least one of the positive electrode and the negative electrode beingcapable of storing and releasing lithium ions, and containing an activematerial that satisfies the following conditions (A) to (D): (A) theactive material being a Li complex oxide or a Li complex oxoacid saltthat contains lithium, oxygen, and at least one of the elements ofGroups 2 to 15 of the long-form periodic table; (B) the active materialcontaining a plurality of primary particles having a particle sizedistribution (median diameter: nm) with 1 nm<D10<65 nm, 5 nm<D50<75 nm,and 50 nm<D90<100 nm; (C) the active material having a plurality ofpores between the plurality of primary particles, wherein the maximumpeak pore size A (nm) in a pore size distribution as measured by amercury intrusion technique is 10 nm≦A≦75 nm; and (D) the ratio B/A ofthe maximum peak pore size A (nm) and the crystallite size B (nm)determined from the half width of the X-ray diffraction pattern of theactive material as measured by X-ray diffractometry is 0.5<B/A≦1.
 2. Thelithium ion secondary battery according to claim 1, wherein the activematerial includes a carbon material-containing coating on at least apart of the surface of the primary particles, the coating having a Ramanspectrum with an intensity ratio (I_(D)/I_(G)) of 0.65 or more between apeak (intensity I_(D)) in a 1,250 cm⁻¹ to 1,350 cm⁻¹ range and a peak(intensity I_(G)) in a 1,500 cm⁻¹ to 1,700 cm⁻¹ range as measured byRaman spectroscopy.
 3. The lithium ion secondary battery according toclaim 2, wherein the weight ratio of the coating with respect to theprimary particles is 0.01 weight % to 10 weight %.
 4. The lithium ionsecondary battery according to claim 1, wherein the active material iscontained in the positive electrode, and has a direct currentresistivity of 7.5 kΩ·cm or less in a charged state with 80% chargedepth.
 5. The lithium ion secondary battery according to claim 1,wherein the active material contained in the positive electrode has alaminar rock salt structure, a spinel structure, or an olivinestructure, and wherein the active material contained in the negativeelectrode has a spinel structure.
 6. The lithium ion secondary batteryaccording to claim 5, wherein the active material contained in thepositive electrode is at least one of the compounds of the formulae (1)to (3) below, and wherein the active material contained in the negativeelectrode is at least one of the compounds of the formulae (4) to (6)belowLi_(a)M1O₂  (1) (where M1 is at least one of the elements of Groups 2 to15 of the long-form periodic table, and a satisfies 0<a≦1.2),Li_(b)Mn_(c)M2_(d)O₄  (2) (where M2 is at least one of the elements ofGroups 2 to 15 of the long-form periodic table (excluding Mn), and b, c,and d satisfy 0<b≦1, 0<c≦2, 0≦d<2, and c+d=2),Li_(e)M3_(f)PO₄  (3) (where M3 is at least one of the elements of Groups2 to 15 of the long-form periodic table, and e and f satisfy 0<e≦1, and0<f≦1),Li[Li_(x)M4_((1−3x)/2)Ti_((3+x)/2)]O₄  (4) (where M4 is at least one ofMg, Ca, Cu, Zn, and Sr, and x satisfies 0≦x≦⅓),Li[Li_(y)M5_(1−3y)Ti_(1+2y)]O₄  (5) (where M5 is at least one of Al, Sc,Cr, Mn, Fe, Ga, and Y, and y satisfies 0≦y≦⅓), andLi[Li_(1/3)M6_(z)Ti_((5/3)−z)]O₄  (6) (where M6 is at least one of V,Zr, and Nb, and z satisfies 0≦z≦⅔).
 7. The lithium ion secondary batteryaccording to claim 6, wherein the M1 is at least one of Ni, Co, Mn, Cu,Fe, Zn, Y, Ti, Mo, Al, Mg, B, V, Cr, Sn, Ca, Sr, and W, wherein the M2is at least one of Co, Ni, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ca,Sr, and W, and wherein the M3 is at least one of Co, Mn, Fe, Ni, Mg, Al,B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr.
 8. An electrode for lithiumion secondary batteries, the electrode comprising an active materialcapable of storing and releasing lithium ions and satisfying thefollowing conditions (A) to (D): (A) the active material being a Licomplex oxide or a Li complex oxoacid salt that contains lithium,oxygen, and at least one of the elements of Groups 2 to 15 of thelong-form periodic table; (B) the active material containing a pluralityof primary particles having a particle size distribution (mediandiameter: nm) with 1 nm<D10<65 nm, 5 nm<D50<75 nm, and 50 nm<D90<100 nm;(C) the active material having a plurality of pores between theplurality of primary particles, wherein the maximum peak pore size A(nm) in a pore size distribution as measured by a mercury intrusiontechnique is 10 nm≦A≦75 nm; and (D) the ratio B/A of the maximum peakpore size A (nm) and the crystallite size B (nm) determined from thehalf width of the X-ray diffraction pattern of the active material asmeasured by X-ray diffractometry is 0.5<B/A≦1.
 9. An active material forlithium ion secondary batteries, the active material capable of storingand releasing lithium ions and satisfying the following conditions (A)to (D): (A) the active material being a Li complex oxide or a Li complexoxoacid salt that contains lithium, oxygen, and at least one of theelements of Groups 2 to 15 of the long-form periodic table; (B) theactive material containing a plurality of primary particles having aparticle size distribution (median diameter: nm) with 1 nm<D10<65 nm, 5nm<D50<75 nm, and 50 nm<D90<100 nm; (C) the active material having aplurality of pores between the plurality of primary particles, whereinthe maximum peak pore size A (nm) in a pore size distribution asmeasured by a mercury intrusion technique is 10 nm≦A≦75 nm; and (D) theratio B/A of the maximum peak pore size A (nm) and the crystallite sizeB (nm) determined from the half width of the X-ray diffraction patternof the active material as measured by X-ray diffractometry is 0.5<B/A≦1.10. An electronic device comprising the lithium ion secondary battery ofclaim
 1. 11. An electric power tool comprising the lithium ion secondarybattery of claim
 1. 12. An electric vehicle comprising the lithium ionsecondary battery of claim
 1. 13. A power storage system comprising thelithium ion secondary battery of claim 1.